Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$193.30	10.359%	$213.3239	$213.32	$213.30	$213.30
Purchase #2	$38.66	7.323%	$41.4911	$41.49	$41.50	$41.50
Purchase #3	$53.67	5.106%	$56.4104	$56.41	$56.40	$56.40
Purchase #4	$80.43	6.255%	$85.4609	$85.46	$85.45	$85.50
Purchase #5	$206.47	13.559%	$234.4653	$234.47	$234.45	$234.50
Purchase #6	$40.89	7.236%	$43.8488	$43.85	$43.85	$43.80
Purchase #7	$149.81	10.489%	$165.5236	$165.52	$165.50	$165.50
7 purchase totals =	$763.23		$840.5240	$840.52	$840.45	$840.50